Method and apparatus for testing bumped die

ABSTRACT

A method and apparatus for testing unpackaged semiconductor dice having raised contact locations are disclosed. The apparatus uses a temporary interconnect wafer that is adapted to establish an electrical connection with the raised ball contact locations on the die without damage to the ball contact locations. The interconnect is fabricated on a substrate, such as silicon, where contact members are formed in a pattern that matches the size and spacing of the contact locations on the die to be tested. The contact members on the interconnect wafer are formed as either pits, troughs, or spike contacts. The spike contacts penetrate through the oxide layer formed on the raised ball contact locations. Conductive traces are provided in both rows and columns and are terminated on the inner edges of the walls of the pits formed in the substrate. This arrangement allows a system to measure the continuity across the bump pad or ball contact locations of the integrated circuit die in order to establish that each solder ball location is properly attached. This allows the system to test for the presence and quality of the bumps or balls on the particular die being tested.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/521,932, filed Mar. 9, 2000, pending, which is acontinuation of U.S. patent application Ser. No. 08/994,004, filed Dec.18, 1997, now U.S. Pat. No. 6,140,827, issued Oct. 31, 2000.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to semiconductormanufacturing and, more particularly, to methods for testingsemiconductor dice having raised or bumped bond pads. More particularlystill, the present invention relates to fabricating and using a testinggrid suitable for testing solder balls used for bumped bond pads on anunpackaged semiconductor die.

[0003] Semiconductor dice are being fabricated with raised bond pads andare known as bumped semiconductor die. A bumped semiconductor dieincludes bond pads along with bumped solderable material such as alead-tin alloy. These typically are manufactured from solder balls madeof a lead-tin alloy. Bumped dies are often used for flip chip bondingwhere the die is mounted face down on the substrate, such as a printedcircuit board, and then the die is attached to the substrate by weldingor soldering. Typically, the bumps are formed as balls of materials thatare circular in a cross-sectional plane parallel to the face of the die.The bumps typically have a diameter of from 50 micrometers (μm) to 100μm. The sides of the bumps typically bow or curve outwardly from a flattop surface. The flat top surface forms the actual region of contactwith a mating electrode on the printed circuit board or other substrate.In testing the attached solder bumps, a temporary electrical connectionmust be made between the contact locations or bond pads on the die andthe external test circuitry associated with the testing apparatus. Thebond pads provide a connection point for testing an integrated circuiton the die. Likewise, the integrity of each bump must be tested as well.

[0004] In making this temporary electrical connection, it is desirableto effect a connection that causes as little damage as possible to thebumped die. If the temporary connection to the bumped bond pad damagesthe pad, the entire die may be ruined. This is difficult to accomplishbecause the connection must also produce a low resistance or ohmiccontact with the bumped bond pad. A bond pad, with or without a bump,typically has a metal oxide layer formed over it that must be penetratedto make the ohmic contact.

[0005] Some prior art contact structures, such as probe cards, scrapethe bond pads and wipe away the oxide layer. This causes excess layerdamage to the bond pads. Other interconnect structures, such as probetips, may pierce the oxide layer and metal bond pad and leave a deepgouge. Still other interconnect structures, such as micro bumps, cannoteven pierce the oxide layer, preventing the formation of an ohmiccontact.

[0006] In the past, following testing of a bump pad die, it has beennecessary to reflow the bumps, which are typically damaged by theprocedure. This is an additional process step that adds to the expenseand complexity of the testing process. Furthermore, it requires heatingthe tested die that can adversely affect the integrated circuitry formedon the die.

[0007] Other bond pad integrity testing systems have been developed inthe prior art. Typically, these testing systems use optical imaging todetermine the integrity of the weld connection on the bumped sites. Onetype of system is a profiling system that uses interferometry withrobotic wafer handling to automate the testing step. The testing stepdevelops a profile for measuring solder bump heights. Unfortunately,although the interferometry system does not damage the device in anyway, the time required for analyzing each bump location can take fromtwo to four minutes. This type of throughput is unacceptable when a highspeed system is necessary.

[0008] Accordingly, what is needed is a method and system for testingsolder bumps in bond pad locations that does not damage the bond padswhile improving throughput.

SUMMARY OF THE INVENTION

[0009] According to the present invention, a method and apparatus fortesting unpackaged semiconductor dice having raised contact locationsare disclosed. The apparatus uses a temporary interconnect wafer that isadapted to establish an electrical connection with the raised ballcontact locations on the die without damage to the ball contacts. Theinterconnect wafer is fabricated on a substrate, such as silicon, wherecontact members are formed in a pattern that matches the size andspacing of the contact locations on the die to be tested. The contactmembers on the interconnect wafer are formed as either pits, troughs, orspike contacts. The spike contacts penetrate through the oxide layerformed on the raised ball contact location. Conductive traces areprovided in both rows and columns and are terminated on the inner edgesof the walls of the pits formed in the substrate. This arrangementallows a system to measure the continuity across the bump pad or ballcontact locations of the integrated circuit die in order to establishthat each ball contact location is properly attached. This also allowsthe system to test for the presence and quality of the bump or ballcontact locations on the particular die being tested.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0010]FIG. 1 is a schematic cross-sectional diagram of a pit formed in asubstrate wherein a solder ball is received;

[0011]FIG. 2 is a cross-sectional perspective schematic view of the pitaccording to FIG. 1;

[0012]FIG. 3 is a top plan view of an array of pits according to that ofFIG. 1 having a metal interconnect in a form of rows and columns;

[0013]FIG. 4 is an alternative embodiment of the pit of FIG. 1 whereinraised supports are provided along with sharp blades for penetrating theball;

[0014]FIG. 5 is an alternative embodiment of the pit of FIG. 1 whereinraised portions are provided for penetrating the solder balls;

[0015]FIG. 6 is an example of a solder ball being out of place andfailing to make adequate connection between adjacent metal bonds;

[0016]FIG. 7 is an example of when a ball that is too small has beenidentified;

[0017]FIG. 8 is a schematic cross-sectional view of a device under testwhere mismatched balls are adjacent to one another; and,

[0018]FIG. 9 is a block diagram of a test apparatus using the bump plateaccording to FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

[0019]FIG. 1 is a cross-sectional schematic view of a bump plate 10 fortesting the connect conductivity and quality of a solder ball on anunpackaged semiconductor die. Bump plate 10 is fabricated in asemiconductor substrate 12, such as, for example, silicon, galliumarsenide, or silicon on sapphire, to name a few.

[0020] A plurality of receiving pits 14 is formed in the surface ofsubstrate 12. Pit 14 can be any desired polygonal or curved shape, butis preferred to be square with four sloped side walls 16. Each wall 16is at an angle of 54° from horizontal, conforming to the plane of thesurface of the silicon substrate that can be used in fabricating bumpplate 10. After pits or suitable features are etched (formed), thesurface of the plate is coated with a thin layer insulator of about200-300 Angstroms (such as Si Oxide) before the metal traces are formed.Electrical connection for testing for the presence of the solder ballson the die is provided by metal traces 18. Metal traces 18 are made froma suitable metal and extend across the surface of substrate 12 and downwalls 16 of pit 14. A solder ball or bump 20 can then be positionedwithin pit 14 and contact all four sloped walls 16. Ball 20 is placedwithin pit 14 when a die under test is mated with bump plate 10. Since ametal trace 18 is placed on each wall 16 and extends across the surfaceof substrate 12 to an adjacent pit 14, an applied electric current canflow through metal traces 18 provided the solder ball 20 contacts bothsides of wall 16 and metal trace 18 thereon.

[0021] A method that is adaptable for manufacturing bump plate 10 isdescribed in U.S. Pat. No. 5,592,736, “Fabricating An Interconnect ForTesting Unpackaged Semiconductor Dice Having Raised Bond Pads,” commonlyassigned to the same assignee as the present invention, and hereinincorporated by reference for all purposes.

[0022]FIG. 2 depicts, in a cross-sectional perspective view, pit 14prior to the addition of metal trace 18 of FIG. 1. Pit 14 has asubstantially flat bottom surface that is non-conductive as well as fouradjacent side walls 16, again having the slope angle that naturallyslopes 54° in the surface plane of silicon substrate 12 as it is etched.The sloped wall 16 allows for a spherical ball 20 to seat within pit 14without damaging the bottom curvature of ball 20 while still contactingmetal trace 18 that extends down the slope of wall 16.

[0023] Bump plate 10 has a plurality of pits 14 and is shown in theschematic diagram of FIG. 3. Bump plate 10 actually is an array of bumppits 14 that is electrically connected in rows and columns using metaltraces 18. Horizontal metal traces 18 run across the surface ofsubstrate 12 and down the sloped walls 16 of the bump pits 14. It isimportant that metal traces 18 do not connect with one another withinpits 14. As an electric current is placed across each row and down eachcolumn in a sequential manner, it becomes readily apparent at each pit14 location whether a ball exists or the connection is of such poorquality as to provide no conduction across the row or down the column.From this information, a grid map of the defects can be established thatwill allow repair of the missing or poor quality bumped locations at asubsequent repair stage.

[0024] Alternative embodiments to pits 14 within the substrate 12 areshown in FIGS. 4 and 5. FIG. 4 illustrates a raised contact location 30for contacting the bottom surface of a solder ball 20. Each raisedcontact location 30 comprises a set of side bumps 32 that form a valley36. A plurality of sharpened projections 34 is formed within valley 36and is designed to pierce the oxide layer formed over ball 20 and can beattached to adjacent metal traces 18 for providing good ohmic contact toadjacent metal traces 18 with ball 20 for testing purposes. Contactlocation 30 can be in the shape of a polygon or circle and can becombined with pits 14 of FIG. 3.

[0025]FIG. 5 is an alternative embodiment where each pit 14 is replacedwith a post trough 40, which is formed by a plurality of posts 42 toform a polygon, such as a square. Posts 42 are formed such that a valley44 is formed in post trough 40. Metal traces are formed up and down thesides of post 42, but not connecting one another in the same manner astraces 18 in FIG. 3. Thus, when a ball 20 is placed in a post trough 40,a good ohmic connection forms between opposite traces 18 for conductinga test current. Further, post trough 40 can be in the shape of a polygonor circle and can be combined with pits 14 of FIG. 3 or contactlocations 30 of FIG. 4.

[0026] Each of the embodiments of FIGS. 1-5 is capable of testing forvarious types of solder ball conditions. The most significant is when amissing ball occurs. This is simple to detect in that no current willflow either across the column or down the row when the test current isapplied. Other examples are also possible and are illustrated in FIGS.6, 7, and 8. FIG. 6 is an example of when a solder ball 20 is off centerand only contacts one or two sides of pit 14, thus preventing a goodcurrent signal from passing either across the column or down the row.FIG. 7 is an example of a ball 20 too small to touch any sides in pit14. In this condition, no current can pass and it is viewed as beingthat no solder ball is present. FIG. 8 depicts where adjacent balls ofdifferent sizes are attached to die 50. A first ball 20 has a firstdiameter and a second ball 52 has a second diameter, which is muchsmaller than the first diameter of ball 20. As is shown, ball 20 is anappropriate size and contacts well with the sides of pit 14. Bycontrast, ball 52 is too small to even reach pit 14, so the currentsignal test shows it as not being present at all. Of course, the reversecan be true in that ball 52 is actually the desired size of the ballswhile ball 20 is an aberration and is much larger than desired. Thiswould be also be evident in that many balls would be seen as not beingpresent as the diameter of ball 20 would prevent several adjacent ballsfrom contacting in their respective pits.

[0027]FIG. 9 depicts a test apparatus 54 that uses a bump plate 10, or abump wafer 10. Apparatus 54 comprises a signal processor, such as acomputer system 56, that attaches to a bump plate 10. Electrical signalsor current are passed to bump plate 10 along the rows and columns of themetal traces 18 to establish a test pattern. A device under test (DUT)58 is pressed upon bump plate 10 to match the solder ball pattern to theidentical pattern fabricated on bump plate 10. Once contact is made, thetest is begun and the results are obtained more quickly compared toprior art test apparatus using optical or other mechanical meanspreviously described.

[0028] The bump die wafer inspection apparatus of the present inventionoffers the following advantages over the prior art. As the electronicworld moves toward stencification miniaturization, better methods fortesting these technologies are needed and this solution provides anadvancement over those previously available and, using semiconductorfabrication techniques, a bump plate matching a desired solder ballpattern for a particular die can be generated. The silicon or othersimilar substrates serve as a rigid medium, and as a result of thisrigidity, they have a fixed dimensional test capability for eachbump/ball testing site. This limits its use with regard to the range ofthe dimensional tolerances that it can test. This is significant in thatthe bumps, or balls, or both, require tight dimensional tolerances topass such testing. The silicon micro-machining and photolithographyprocesses allow much more precise geometry control than the printedcircuit board (PCB) or film technologies found in the prior art. Hence,a more definitive distinction and grading is made for each ball shapeand position. Additionally, the present apparatus provides a uniquemethodology for electronically mapping the failing ball sites and thenutilizing this map to direct a repair or rework system to correct eachfailing site. These operations of testing, mapping, and subsequentrepair can be combined in a highly automated in-line process, thusreducing the necessary steps previously required in the prior art ofremoving the bad boards and sending them to the rework section of thefabrication operation.

[0029] Another advantage is since the semiconductor substrate can beplanarized to a uniform flatness compared to the PCB and otherprocessing solutions, less damage is caused to the good solder ballsattached to the DUT.

[0030] Thus the invention provides an improved method and system fortesting a discrete, unpackaged semiconductor die having raised bondpads. Although specific materials have been described, it is understoodthat other materials can be utilized. Furthermore, although the methodof the invention has been described with reference to certain specificembodiments as will be apparent to those skilled in the art,modifications can be made without departing from the scope of theinvention as defined in the following claims.

What is claimed is:
 1. An interconnect bump plate fabricated to testcontinuity of a plurality of contact bumps on an unpackagedsemiconductor die, said bump plate having an upper surface, theinterconnect bump plate comprising: a plurality of contact receivingsites, said plurality of contact receiving sites fabricated extendinginto portions of said bump plate below said upper surface thereofcorresponding to a size and spacing pattern established by saidplurality of contact bumps on said unpackaged semiconductor die; and aplurality of metal traces for each site of said plurality of contactreceiving sites to contact a corresponding contact bump of saidplurality of contact bumps received at each contact receiving site. 2.The interconnect bump plate according to claim 1, wherein said pluralityof metal traces form a connected array of rows and columnsinterconnecting each contact receiving site to at least one adjacentcontact receiving site of said plurality of sites.
 3. The interconnectbump plate according to claim 1, wherein said plurality of contactreceiving sites comprises a plurality of pits fabricated in asemiconductor substrate having opposing walls wherein said plurality ofmetal traces extend down said opposing walls, but do not contact oneanother.
 4. The interconnect bump plate according to claim 1, whereinsaid plurality of contact receiving sites includes: a plurality ofrisers, over which said plurality of metal traces extend; and aplurality of blades, situated between said plurality of risers, topierce an oxide layer on said corresponding contact bump.
 5. Theinterconnect bump plate according to claim 1, wherein said contactreceiving site is comprised of: a plurality of retaining posts, overeach of which extends one of said plurality of metal traces and in whicha bump seat is formed for receiving said corresponding contact bump. 6.The interconnect bump plate according to claim 1, wherein each of saidplurality of metal traces comprises a unitary metal trace.